If Nolan thinks of Marks mom as a pet, yet had sex with her and made a child with her, then what is the standard for pets on Viltram… Either theirs just a bunch of random species of people who are kept as pets, or they have normal pets(for them) and… um… do things… with. them…
If you’re willing to keep a slave, which is pretty consistent with what we know of how Viltrumites think, it might not occur to you that making a kid with one is weird even though you’re claiming the enslaved people deserve it for “not being people”. Slave owners are ignorant, you can’t expect consistent logic. 🙂